Current consumption reduction with low power amplifier

ABSTRACT

A transceiver circuit and a method in a wireless communication network are provided, where a signal power level for a signal received at the transceiver circuit is measured and compared to a predefined threshold power level. At least two groups of power amplifiers may be used, where one group is optimized for high efficiency above the predefined threshold power level, and one group is optimized for high efficiency below the predefined threshold power level. The amplifiers may be used to amplify the received signal depending on the signal power level in relation to the predefined power threshold level. The signal may then be filtered by duplex filters and forwarded to a diversity antenna or a main antenna where it is transmitted over an air interface.

TECHNICAL FIELD

The present invention relates to current consumption reduction inwireless communication networks.

BACKGROUND OF THE INVENTION

The development of 3G wireless communication networks by standards, suchas HSPDA (High Speed Packet Data Access), EUL (Enhanced Uplink) willallow for higher data rates on the downlink channel (from the basestation to the mobile station) and on the uplink channel (from themobile station to the base station) and further on towards LTE/SAE(Long-Term Evolution/System Architecture Evolution).

HSPDA will for example allow for peak data rates up to 10 Mbit/s,shorter connection and response times and a huge increase in sectorthroughput, while the EUL will increase uplink data rates in a laterHSPDA release. LTE/SAE, in turn, will offer similar advantages.

Nonetheless, while these advantages will benefit end-users and the useof resource hungry mobile applications, the improvements are in conflictwith other parameters important in such wireless communication networks,such as current consumption both in the mobile stations and the basestations, volume, and others.

One attempt of dealing with the increased power consumption is theintroduction of power amplifiers adapted to have high efficiency at highoutput powers and power amplifiers with high efficiency at lower outputpowers as shown in FIG. 1.

Here, the amplifier circuit comprises one amplifier for high outputpower and one for lower output powers, i.e., around 15 dBm. Even thoughthe current consumption through this arrangement is reduced with respectto only one power amplifier, there is still room for reducing thecurrent consumption even more and particularly for saving battery powerin diversity systems, be it in receiver or transmitter diversitysystems, or both.

Aspects of the invention provide an alternative way of reducing thecurrent consumption in a mobile station or an access point in a wirelesscommunication network.

SUMMARY OF THE INVENTION

One aspect of the invention provides a transceiver for wirelesscommunication networks. The transceiver comprises: at least onetransceiver module for determining the signal power to be transmitted; aunit for directing one or more signals whose determined signal power isabove a certain power threshold to one or more first amplifiers withhigh efficiency above the power threshold and one or more signals whosedetermined signal power is below the power threshold to one or moresecond amplifiers with high efficiency at signal powers below the powerthreshold; an isolation arrangement connected to the one or more firstamplifiers for preventing signal reflections of the signals amplified bythe one or more first amplifiers; and at least one first diversityantenna and at least one first main antenna for transmitting theamplified signals.

One advantage of the transceivers according to the present invention isthe tangible reduction in current consumption and the flexibility of itsuse in virtually any diversity transceiver circuit.

Furthermore, another aspect of the invention provides a method foramplifying signal in a wireless communication network which comprisesthe steps of: a) receiving one or more signals, b) determining the powerat which the one or more received signals are to be sent, c) comparingthe power at which the which the one or more received signals are to besent to a predefined power threshold, d) directing one or more signalswhose power is above a certain power threshold to one or more firstamplifiers with high efficiency above the power threshold power, and oneor more signals below the power threshold to one or more secondamplifiers with high efficiency at signal powers below the powerthreshold, e) amplifying the signal in the one or more first amplifiers,f) sending the amplified signal to at least one first diversity antennaor to at least one main antenna and g) transmitting the one or moresignals over the radio interface via the at least one first diversityantenna or at least one first main antenna.

The method may be specially adapted to be implemented by the transceiveraccording to the present invention. Also, the steps of the methodaccording to the present invention may be executed by a computer programrunning either on the transceiver of the present invention or on aseparate storage medium.

BRIEF DESCRIPTION OF THE DRAWINGS (OPTIONAL)

FIG. 1 illustrates an amplifier circuit according to known technology.

FIG. 2 illustrates a transceiver circuit according to a first embodimentof the present invention.

FIG. 3 illustrates a transceiver circuit according to a secondembodiment of the present invention, where the transceiver comprises aDPDT switch.

FIG. 4 illustrates a transceiver circuit in a MIMO (Multiple InputMultiple Output) or MISO (Multiple Input Single Output) system accordingto a third embodiment of the present invention.

FIG. 5 illustrates the steps of a method according to one embodiment ofthe present invention.

FIG. 6 shows a probability versus output power distribution in aCDMA2000 network.

FIG. 7 shows a graph where the current consumption is shown as afunction of output power for a transceiver according to the presentinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following detailed description, reference numbers depictingidentical elements in different figures will not be repeated for eachfigure for the purposes of easier reading.

FIG. 1 gives an illustration of an amplifier circuit 100 where it isattempted to reduce the current consumption in a mobile station or basestation according to known technology.

Referring to FIG. 1, an RF input signal 110 is fed into a splitter 140and directed to the input of a first power amplifier 150 and a secondamplifier 160. The first amplifier 150 is trimmed for high efficiency athigh output powers, while the second amplifier 160 is adapted for highefficiency at lower output powers, such as, for example, 15 dBm orlower.

Depending on whether it is desired to output only the high poweramplified RF signal from the first amplifier 150 or the lower poweramplified RF signal from the second amplifier 160, a mode splitter 110uses a control signal to make either the first amplifier 150 or thesecond amplifier 160 output the amplified signal. The two controlsignals used for controlling the power amplifier outputs are a firstmode signal 120 and a second mode signal 130 corresponding to high powerRF signals and lower power RE signals. Naturally, it may also bepossible to combine both the amplified high power part of the input RFsignal and the lower power part RE input signal in a combiner 170 in anamplified RE output signal 180.

It should be noted that normally, the transceiver according to thepresent invention illustrated in FIGS. 2-5 may be implemented in anymobile device operating in a wireless communication network, such as amobile station, a wireless network card, PDA and similar devices, aswell as in a base station, access point, Node B or similar access pointsin a wireless communication network.

Turning now to FIG. 2, a transceiver circuit 200 according to a firstembodiment of the present invention is shown.

The transceiver circuit 200 comprises a diversity transceiver module 212which among other things is used for determining the power level atwhich an incoming signal is going to be transmitted. Furthermore, thediversity transceiver module 212 is connected to a first group of poweramplifiers (in this case three) 220, 222, 224 trimmed for highefficiency at high output powers, such as, for example 24 dBm or above.Also, the first group of power amplifiers 220, 222, 224 for high outputpowers are each connected to a first group of circulators 230, 232, 234having among other things the function of an isolator for preventingsignal reflections of an RF signal from the first antenna circuit 246.Using a circulator as an isolation circuit would reduce the output powerby approximately 0.4 dB

Each circulator 230, 232, 234, is in turn connected to a first group ofduplexers 240, 242, 244 which may comprise band pass filters for signalsto be transmitted over the air interface and band pass filters forsignals received over the same. These duplexers additionally providehigh isolation between bands of interest and are therefore used forfiltering the interesting part of the signal.

It should be mentioned here, that it is assumed that the signals to beamplified are Wideband Carrier Division Multiplex Multiple Access(WCDMA) or 3G signals to be sent over the air interface. However, it isalso possible to feed combined GSM/EDGE and WCDMA signals as well asLong Term Evolution (LTE)-signals, such as Orthogonal Frequency DivisionMultiplex (OFDM) or Single Carrier—Frequency Division Multiple Access(SC-FDMA) to the first group of power amplifiers 220, 222 and 224 if thebandpass frequency filters 236, 237 and 238 are designed with a wideenough pass band.

Alternatively, the GSM/EDGE signals 249 which are not be amplified bythe first group of power amplifiers 220, 222, 224 are fed directly intoa diversity front-end module or, for example, a SPnT switch 246 beforethey are to be sent over the air interface via the diversity antenna248. Here an SPnT switch is a Single Pole N Throw switch, N being thenumber of switching positions for the switch.

Also, the amplified and filtered radio signals are fed into thediversity front-end module 246 and sent over the air interface via thediversity antenna 248.

Furthermore, radio signals received from the diversity antenna 248 arefiltered by the same first group of frequency filters 236, 237, 238 asabove for removing undesired parts of the frequency spectrum before theyare sent to the transceiver diversity module 212 via the connections240, 242 and 244.

The main transceiver module 252 is connected in a very similar way tothe second front-end module 286. In this case however, since the outputpower for the radio signals amplified in a second group of amplifiers260, 262, 264 is lower than the output power for the radio signalsamplified by the first group of amplifiers 220, 222, 224, isolators inthe form of circulators are not needed. It may be added that the loweroutput power for the amplified radio signals reduces the AdjacentChannel Leakage Ratio (ACLR) and the Error Vector Magnitude (EVM), whichdescribe the interference from neighboring channels to the amplifiedradio channel and the modulation distortion induced by the interferencefrom other channels.

It should also be mentioned that the second group of amplifiers 260,262, 264 are trimmed for high efficiency at lower power levels, such as,for example, 15 dBm or lower.

Additionally, the second group of amplifiers 260, 262, 264 is in turnconnected to a second group of bandpass frequency filters 270, 272, 274.As described previously, these bandpass filers filter the interestingparts of the frequency spectrum for the amplified radio signals beforethey are sent to the main front-end module 286 and further over theradio interface via the main antenna 288.

Radio signals received on the main antenna 288 are also bandpassfiltered by the second group of bandpass frequency filters before beingforwarded as filtered signals 280, 282, 284 to the main transceivermodule 252.

GSM/EDGE signals 290 not intended to be amplified by the second group ofamplifiers 260, 262, 264 are fed via a separate input into the mainfront-end module and sent over the radio interface via the main antenna288. In case only WCDMA signals are to be amplified by the first groupof amplifiers 220, 222, 224 and the second group of amplifiers 262, 264,266, GSM/EDGE signals are fed out from the main front-end module 286 viaa separate output 292.

The transceiver circuit 200 in FIG. 2 was described as a diversitytransceiver circuit. However, it would be equally possible to arrangethe transceiver circuit as only having receiver diversity, which wouldnecessitate a third antenna acting as a transmitting antenna. Thedetails of such a transceiver circuit will not be explained here, sinceit is assumed that they would be known to the skilled person havingaccess to this disclosure.

FIG. 3 illustrates a transceiver circuit 300 according to a secondembodiment of the present invention. Essentially, it is the sametransceiver circuit 200 from FIG. 2 with the addition of a switch 320,which, for example may be a Double Pole Double Throw (DPDT) switch. Thefunction of the elements present from FIG. 2 present in FIG. 2 will notbe repeated here.

A DPDT switch usually consists of two switches switching between twowell-defined states as is known to the skilled person. The DPDT switch320 may be provided as a solid state switch or as an electrical switch,as preferred.

DPDT switch 320 may, depending on the control signal 310 activate themain antenna 288 and put the diversity antenna 248 to ground 310, 312 orvice versa. In this fashion, the active antenna will not be influencedby the other antenna and will therefore see more ground. One reason whyit may be desirable for one of the antennas to see more ground is thatin antenna design, a larger ground plane will result in more gain fromthe antenna connected to the ground plane, which in this specific casemay either be the diversity antenna of the main antenna. This would alsohave the advantage that in small mobile stations where the ground planeis small or limited due to the physical dimensions of the mobilestation, a ground plane extended by the switch would result in betterantenna gain.

The active antenna may be coupled to one of the transceiver circuits;either the main transceiver circuit or the diversity transceivercircuit. However, it may also be possible to couple one of the antennasto the outputs of both transceiver circuits by using other types ofswitches.

Additionally, one may use other types of switches, such as a Singe PoleSingle Throw (SPST) switches, (Double Pole Double Throw (DPDT) switches,Single Pole Double Throw (SPDT) switches, Single-Pole Change Over (SPCO)switches and other types of switches suitable for switching between theone first diversity antenna and the one first main antenna.

Turning now to FIG. 4, a transceiver circuit 400 according to a thirdembodiment of the present invention is illustrated. In this embodiment,we have the same transceiver as in FIG. 2 applied to a multiple input,multiple output (MIMO) or a multiple input, multiple output (MISO)system.

In contrast to the embodiments in FIGS. 2 and 3, each front end module246, 286 has its own receiver antennas 248, 288 and transmitter antennas448, 488. Thus, since signals are transmitted and received via differentantennas, frequency filters 236, 237, 238 and 270, 272, 274 forseparation of uplink from downlink signals are no longer needed.

The example MIMO or MISO transceiver system 400 may of course comprisemore than two sets of receiver and transmitter antennas 248, 288 and448, 488, depending on the application.

FIG. 5 illustrates the steps of a method according to one embodiment ofthe present invention. At step 500, one or more signals are received ata transceiver circuit which may be one of the transceiver circuits 200,300 or 400 described above or some modification of these circuitsconsistent with aspects of the transceiver circuits described above andconsistent with the present invention.

Next, at step 510, in one of the transceiver modules 212, 252 the powerlevel at which the one or more received signals are to be transmitted,is determined. This may however be done earlier in a DC/DC converterbefore the signal has arrived at one of the transceiver modules (notshown). Thereafter at step 520, the determined signal power level forthe one or more received signals is compared with a predefined thresholdpower value. This threshold power value is chosen so that the first onegroup of amplifiers 220, 222, 224 is adapted to have maximum efficiencyabove this value, while the second one group of amplifiers 260, 262, 254is adapted for maximum efficiency below the threshold power value. Thecomparison step 520 is needed to determine to which group of amplifiersthe one or more signals should be sent in order to be amplified.

Therefore, if the signal power value for the one or more receivedsignals is above the predefined threshold value it is sent to the firstone group of amplifiers 220, 222, 224 at step 530

Thereafter, at step 540 the one or more received signals are amplifiedby the first one group of amplifiers 220, 222, 224 and sent further atstep 540 to the diversity antenna 248 where they are transmitted overthe air interface at step 550.

In contrast, if the signal power for the one or more received signals isdetermined to be below the predefined threshold power value, the one ormore received signals are forwarded to the second one group ofamplifiers 260, 262, 264 at step 525. Thereafter, the one or moresignals are amplified by the second group of amplifiers 260, 262, 264 atstep 535 and sent to the main antenna 288 at step 545.

It will be appreciated here, that in at least one embodiment of thetransceiver according to the present invention (e.g., the secondembodiment), the amplified one or more signals may be sent to either thediversity antenna 248 or the main antenna 288, as preferred.

Finally, at step 550 the thus amplified one or more signals aretransmitted over the air interface via the main antenna 288.

FIG. 6 illustrates a probability versus output power distribution 610taken from suburban profile measurements for the CDMA2000 system. Thediagram shows the probability in percent of a certain output powerexpressed in dBm. Values above 24 dBm are not shown due to the powerclass constraints, meaning a transceiver sending WCMDA signals is notallowed to send signals with higher than 24 dBm +1/−3 dB (power class 3constraint). As can be seen from the diagram, the output power will bemostly concentrated between −20 dBm and 15 dBm with a slight tailbetween 15 dBm and 25 dBm.

These figures are known to the skilled person and have been arrived atby experiment in many wireless networks in dedicated mode and are usedin cell planning.

Using these figures however, simulations on the transceiver circuitaccording to the present invention have been performed with varyingmaximum power values for which the efficiencies of second group of poweramplifiers 260, 262, 264 have been optimized.

The result of these simulations is shown in the graph in FIG. 7.Referring to FIG. 7, the graph shows the current consumption in mA as afunction of output power in dBm for three scenarios. The first scenariocomprised the use of a single power amplifier with maximum efficiency atmaximum power and is illustrated by the curve 710.

It is evident that the current consumption lies around 0.8 mA for anoutput power in the interval −18 dBm to 16 dBm, while it rapidly risesbetween for output powers beyond 16 dBm.

The second scenario comprised two power amplifier groups, where thefirst group comprised power amplifiers trimmed for high efficiency atoutput powers above 15 dBm and power amplifiers trimmed for highefficiency at output power up to 15 dBm which is illustrated by thecurve 720.

It is clearly visible that the average current consumption in theinterval between −18 dBm and 15 dBm lies around 0.2 mA, before rapidlyrising for an output effect beyond 15 dBm in a similar way as for thefirst scenario. The sudden jump in current consumption in the regionbetween 15 dBm and 17 dBm may be explained by the fact that in thisregion the amplification switches from the lower power Power amplifier(PA) to the high power PA.

Finally, the third situation comprised a high power PA and a lower powerPA with trimmed efficiency up to 9 dBm represented by the curve 730.

The sudden increase in current consumption is similar to the secondscenario but (logically) kicks in between 9 dBm and 11 dBm. Later on, ataround 16 dBm output power, the increase in current consumption becomesidentical to the first and second scenarios.

Using known formulas for calculating the current consumption probabilityfor all three scenarios, it was found that the average currentconsumption for the second and third scenarios where lower power PAoptimized for high efficiency at lower powers are used, was reduced by16 mA compared to the case of only one power amplifier at maximum outputpower. However the difference in current consumption between the secondand third cases was only marginal.

It may be added that the transceiver according to the present inventionmay be employed in any wireless communication system, such as, forexample, GSM, WCDMA, CDMA2000, Wireless Local Area Network (WLAN SPST),such as IEEE 802.11a, IEE 802.11b, IEEE 802.11g, HiperLAN, WINNER, WiMAXand other similar wireless communication systems.

Also the power amplifiers may consist of one amplifier component whichusually is a solid state component, or comprise more than one amplifiercomponent, depending on need. Although some power levels at which thepower amplifiers have been designed to be highly efficient have beenmentioned earlier in the description, they are given as example valuesonly. It should be understood that the specific power levels for whichthe PAs are designed to be highly efficient depend on the applicationfield and therefore may vary.

It should be emphasized that the term “comprises/comprising” when usedin this specification is taken to specify the presence of statedfeatures, integers, steps, or components, but does not preclude thepresence or addition of one or more other features, integers, steps,components, or groups thereof.

No element, act, or instruction used in the description of the presentapplication should be construed as critical or essential to theinvention unless explicitly described as such. Also, as used herein, thearticle “a” is intended to include one or more items. Where only oneitem is intended, the term “one” or similar language is used. Further,the phrase “based oil,” as used herein is intended to mean “based, atleast in part, on” unless explicitly stated otherwise.

The scope of the invention is defined by the claims and theirequivalents.

1. A transceiver for a wireless communication network, comprising atransceiver module for determining the signal power to be transmitted; aunit for directing one or more signals whose power is above a certainpower threshold to one or more first amplifiers with high efficiencyabove the power threshold and one or more signals below the powerthreshold to one or more second amplifiers with high efficiency atsignal powers below the power threshold; an isolation arrangementconnected to the one or more first amplifiers for preventing signalreflections of the signals amplified by the one or more firstamplifiers; and at least one first diversity antenna and at least onefirst main antenna for transmitting the amplified signals.
 2. Thetransceiver according to claim 1, wherein the one or more firstdiversity and first main antennas are arranged for receiving signalsfrom other devices in the communication network.
 3. The transceiveraccording to claim 2, wherein the transceiver further comprises filtersfor separating signals to be transmitted via the one first diversityantenna and one first main antenna from signals received via the onefirst diversity antenna and one first main antenna.
 4. The transceiveraccording to claim 1, wherein the transceiver further comprises filtersfor separating signals to be transmitted via the one first diversityantenna and one first main antenna from signals received via the onefirst diversity antenna and one first main antenna.
 5. The transceiveraccording to claim 1, wherein the transceiver further comprises at leastone second diversity antenna and at least one second main antenna forreceiving signals from other devices in the communication network, 6.The transceiver according to claim 1, wherein the transceiver furthercomprises a switch for selecting either the one first diversity antennaor the one first main antenna for transmitting the one or more signalsamplified either by the one or more first amplifiers or by the one ormore second amplifiers.
 7. The transceiver according to claim 6, whereinthe switch is arranged to select one of the first diversity antennas orone of the first main antennas and connect the other antenna to ground.8. The transceiver according to claim 7, wherein the switch is one of asinge pole single throw switch, a double pole double throw switch, asingle pole double throw switch, a single pole change over switch orother type of switch suitable for changing between the one firstdiversity antenna and the one first main antenna.
 9. The transceiveraccording to claim 8, wherein the signals amplified by the at least oneor more first amplifiers and the at least one or more second amplifiersare wideband carrier division multiple access (WCDMA) signals, orcombined global system for mobile communications/enhanced data rates forGlobal Evolution (CSM/EDGE) and WCDMA signals.
 10. The transceiveraccording to claim 6, wherein the switch is one of a singe pole singlethrow switch, a double pole double throw switch, a single pole doublethrow switch, a single pole change over switch or other type of switchsuitable for changing between the one first diversity antenna and theone first main antenna.
 11. The transceiver according to claim 1,wherein the signals amplified by the one or more first amplifiers andthe at least one or more second amplifiers are WCDMA signals, orcombined GSM/EDGE and WCDMA signals.
 12. A method for amplifying signalin a wireless communication network, comprising: receiving one or moresignals; determining the power at which the one or more received signalsare to be sent; comparing the power at which the which the one or morereceived signals are to be sent to a predefined power threshold;directing one or more signals whose power is above a certain powerthreshold to one or more first amplifiers with high efficiency above thepower threshold power, and one or more signals below the power thresholdto one or more second amplifiers with high efficiency at signal powersbelow the power threshold; amplifying the signal at the one or morefirst amplifiers; sending the amplified signal to at least one firstdiversity antenna or to at least one main antenna; and transmitting theone or more signals over the radio interface via the at least one firstdiversity antenna or at least one first main antenna.